Consider the following diagram (Section 3 in [1]})
\({E_{{\mathbf {V}}_{\alpha }}\times E_{{\mathbf {V}}_{\beta }}&E_{\alpha ,\beta }^{\prime }[l]_-{p_{1\alpha ,\beta }}[r]^-{p_{2\alpha ,\beta }}&E_{\alpha ,\beta }^{\prime \prime }[r]^-{p_{3\alpha ,\beta }}&E_{{\mathbf {V}}_{\alpha +\beta }}}.\) 
